Preheat oven to 180°C/160°C fan-forced. Line a 12-hole, ⅓ cup-capacity muffin pan with paper cases.
Combine flour, cocoa powder, sugar and dark chocolate bits in a large bowl. Make a well in centre. Whisk vegetable oil, milk, vanilla and eggs in a large jug. Add oil mixture to well (see Cooking class, below). Using a wooden spoon, stir until just combined (don't over-mix). Spoon mixture into paper cases.
Bake for 25 minutes or until firm to touch and a skewer inserted into the centre comes out clean. Stand in pan for 5 minutes. Transfer to a wire rack to cool. Serve.
